-LRB- CNN -RRB- -- Syria was plunged Wednesday into a nationwide blackout , the state-run Syrian Arab News Agency reported .

A `` terrorist attack on the gas feeder line for a power plant '' in southern Damascus led to `` power outages in all provinces '' and efforts were under way to restore it , Electricity Minister Imad Khamis told SANA .

Syrian activists were posting video to social media accounts showing what they described as a gas line fire near the Damascus airport . The video showed unidentified buildings in the dark , with a fire burning on higher ground behind the structures .

And the Syrian Observatory for Human Rights reported that a large explosion rocked Damascus late Wednesday . The blast targeted a government checkpoint and injured soldiers there , the London-based activist group said .

In London on Wednesday , at a meeting of the `` Friends of Syria , '' the head of Syria 's main opposition umbrella group laid out a list of conditions for participation in a conference to be held by the end of the year in Geneva with the goal of ending the bloodshed that has wracked the country since March 2011 .

Ahmad al-Jabra , leader of the Syrian National Coalition , said they include :

-- releasing prisoners ;

-- lifting the siege from affected areas and allowing the entry of aid ;

-- stopping the use in civilian areas of ballistic missiles , cluster bombs and fighters jets ;

-- the departure from Syria of Hezbollah and Iranian Revolutionary Guard forces ;

-- the renewal without conditions of ex-pats ' Syrian passports ;

-- a commitment from President Bashar al-Assad to implement the provisions reached in the first such conference , dubbed Geneva 1 ;

-- a declaration by al-Assad to accept a transition of power to an interim government body with executive powers , written in the constitution ;

-- an agreement by all sides that the transitional government is the sole source of legitimate law in the country ;

-- an agreement that the U.N. Security Council will guarantee any agreement under Chapter VII of its charter , which would allow military action ;

-- a timetable for the transition ;

-- stipulation that those responsible for war crimes against humanity be removed from power and held accountable .

British Foreign Minister William Hague told reporters Wednesday that al-Assad should play no political role in Syria .

The opposition Local Coordination Committees of Syria said at least 33 people were killed Wednesday across Syria .

State-run SANA said at least 10 people were killed in `` terrorist '' attacks in Damascus and Aleppo .

CNN 's Hamdi Alkhshali and Salma Abdelaziz contributed to this report

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NEW : A large explosion rocked Damascus,Syria-focused human rights group says

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State-run news agency cites a `` terrorist '' attack on a power plant in southern Damascus

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Activists post video of fire

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In London , the main opposition umbrella group lists conditions for a planned conference